2 relays to turn on LED

Discussion in 'The Projects Forum' started by bamot, Jun 3, 2014.

  1. bamot

    Thread Starter New Member

    Jun 3, 2014
    Hi, i need a little help to find a solution, that i couldn't found.

    I need to turn on and off a LED with only one pushbutton. When the LED is off when i press the pushbutton the LED must be always on until i press the pushbutton again to turn it off.

    I need to know and how is possible to do that using only 2 Relay with 5 pin, one LED and one pushbutton.

  2. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    It can't be done.
    A relay with 5 pins is an SPDT relay (Single Pole Double Throw). To accomplish what you are looking for, the relays need a minimum of 8 pins which is a DPDT (Double Pole Double Throw).
    See the image below:
  3. Alberto

    Active Member

    Nov 7, 2008
  4. Taqhi

    New Member

    Oct 2, 2010
    Why do not you use JK flip flop and set the k=1 and J as a push button. That is in toggle mode. The JK FF will latch and will toggle when you press the pushbutton.
  5. Taqhi

    New Member

    Oct 2, 2010
    If you insist using a relay then you could use the Q of the FF and 2.2K ohm resistor connected to the base of an NPN transistor. The relay's coil need to be connected to the collector of NPN transistor and the other end of the coil to the +V depend on your relay energizing voltage requirement. Then you can use the pins of the relay.
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    What about an alternate-action pushbutton? No relays, no logic.

    ErnieM and wayneh like this.
  7. bamot

    Thread Starter New Member

    Jun 3, 2014
    Thanks all for your help. The pushbutton have another function that's why i have to use a pushbutton.
    About the scheme of djsfantasi i will have a try.
    I will also search and try the JK flip flop.
    About the pulsed relay is too expensive compared to 2 relay dpdt and must be a low cost solution.
  8. eetech00

    Active Member

    Jun 8, 2013
    Take a look at this chip:

    http://media.digikey.com/pdf/Data Sheets/Atmel PDFs/U6032B.pdf

    You could use this chip with a relay.